Rapid Loss of Perennial Alpine Ice Patches, Selwyn and Mackenzie Mountains, NWT. [2019]
Editor’s Note - In this article, Glen MacKay, Leon Andrew, Naomi Smethurst and Thomas D. Andrews highlight the importance of the ice patches in the Selwyn and Mackenzie Mountains. Through core samples and the melting process of the ice patches, scientists are able to gather important information on the animals and hunters that relied on these patches. So what happens when they’re gone? Read on for more info…
This article first appeared in the newly released 2019 State of the Mountains Report. We'll continue to publish articles exploring the science on our current state of Canada's alpine on our blog throughout the year. Find them all here.
Figure 1 – Researchers work at alpine ice patch KfTe-1 in 2007, which had nearly completely melted by 2017. Photo by Tom Andrews/GNWT.
Visiting the disappearing KfTe-1 ice patch
On August 16, 2017, we made our annual visit to an alpine ice patch known as KfTe-1 as part of the Northwest Territories (NWT) Ice Patch Monitoring Program in the Selwyn and Mackenzie Mountains. Our project team – a long-term partnership between archaeologists from the Prince of Wales Northern Heritage Centre and Shúhtagot’ine Elders from the Tulita Dene Band – had stopped at this site almost every year since 2005 to observe its condition and collect archaeological artifacts and biological specimens melting out of the ice (Figure 1). We were struck by how different the ice patch looked compared to past visits. Although it was still obscured by a thin skiff of snow left over from the winter snowpack, it was apparent that the underlying ice had deteriorated significantly. When we returned from the field, we continued to monitor KfTe-1 using publicly available imagery from the European Space Agency’s Sentinel-2 satellite. By October 1, the snow from the previous winter had melted away, and it looked like the underlying ice patch had almost completely disappeared.
significance of the Selwyn and Mackenzie Mountain ice patches
Alpine ice patches in the Selwyn and Mackenzie Mountains hold an incredible archive of the millennia-long relationship between perennial ice, northern mountain caribou, and pre-contact Shúhtagot’ine hunters.1 Caribou seek out ice patches on hot summer days to cool off and escape the hordes of parasitic and biting insects that infest the alpine tundra and forests. Melting ice patches are ringed by a thick black band of caribou dung accumulated by many generations of caribou. For human hunters, ice patches were predictable places to find and kill caribou during the summer, and now, melting ice patches are revealing perfectly preserved hunting weapons – some thousands of years old – that were lost or abandoned during the hunt (Figure 2). Ice patches do a good job of preserving artifacts and biological material not only because they are frozen, but also because they are relatively static. Like glaciers, ice patches accumulate through winter precipitation, forming over time as wind-blown snow builds up on the leeward slopes of mountains.2 Perennial ice patches tend to form on north-facing slopes, where the snow drifts are most protected from direct sunlight. In contrast to glaciers, they do not typically obtain enough mass to move downslope, meaning that fragile artifacts are not crushed or ground to pieces by physical movement of the ice.
Figure 2 – Archaeological artifacts collected from melting ice patches in the Mackenzie and Selwyn Mountains: a) Detail of a complete arrow (approx. 340 years old); b) Dart point with attached sinew (approx. 2,400 years old); c) Detail of a ground squirrel snare (approx. 1,000 years old). Photos by Susan Irving/GNWT. Layout assistance by Dot Van Vliet, GWNT.
Learning about caribou and other animals through core samples
At KfTe-1, one of the oldest known ice patches in the Selwyn Mountains, this repeated pattern of winter snow accumulation and summer use by caribou has created stratified layers of ice separated by thin lenses of caribou dung. In 2008, a 3.5-metre-long ice core extracted from the thickest section of KfTe-1 revealed eight distinct layers of dung that dated sequentially from about 700 to nearly 5,000 years ago.3 Scientists have used these frozen dung layers to study patterns of caribou diet over time, climatic and vegetation changes in the alpine landscape, and even ancient plant-infecting viruses.4,5 Researchers have also used ancient DNA extracted from caribou bones collected from ice patches to study the population dynamics of caribou in the Selwyn and Mackenzie Mountains.6
In addition to being valuable archaeological and environmental archives, alpine ice patches are also ecological hotspots in the alpine landscape. While the link between mountain caribou and ice is the most important dynamic at these sites, ice patches also provide habitat for small mammals and birds, such as marmots, ground squirrels and ptarmigan. One of the most unique artifacts collected from KfTe-1 is a thousand-year-old ground squirrel snare that was likely set by hunters while they were waiting for caribou (see Figure 2). Wolverine bones and wolf feces found at KfTe-1 indicate that ice patches are also important for scavengers and predators.
Melting ice patches and what will happen when they’re gone
“Fragile archaeological artifacts released from the ice will degrade rapidly if they are not immediately collected.”
If KfTe-1 is indeed on the precipice of melting completely away, it will mean that it has melted more over the last few years than it has in approximately 5,000 years. This rapid loss of perennial ice patches is not unprecedented in the Selwyn and Mackenzie Mountains. Between 2009 and 2011, we witnessed the demise of a smaller ice patch called KhTe-2 (Figure 3). An ice core extracted from this site in 2007 showed that at least part of the ice patch was close to 3,000 years old.7 Surprised by its rapid loss, we hypothesized a tipping point at which the amount of heat absorbed from the sun by the ever-increasing amounts of black dung exposed at the edges of the melting ice patch accelerated the melting of the remaining ice.
Figure 3 – Rapid melt of KhTe-2 occurred between 2009 and 2011. By 2011, all that was left of the patch was a 300-metre-long streak of caribou dung across the mountainside. Photos by Tom Andrews/GNWT.
With climate change tipping the balance towards the catastrophic melt of alpine ice patches, it is important to take stock of what will be lost. Fragile archaeological artifacts released from the ice will degrade rapidly if they are not immediately collected. At large ice patches like KfTe-1, the stratified dung layers will collapse into a single layer, making them much less useful for studying environmental change through time. Important relief habitat for mountain caribou will also be lost at a time when they are already trying to adapt to a rapidly warming alpine environment. The rapid loss of alpine ice patches in the Selwyn and Mackenzie Mountains highlights the need for sustained research on ice patches wherever they may exist in Canada’s mountain ranges.
Glen MacKay is the Territorial Archaeologist with the Government of the Northwest Territories, based at the Prince of Wales Northern Heritage Centre in Yellowknife. MacKay has participated in the NWT Ice Patch Project since 2005. Leon Andrew is a widely respected Shúhtagot’ine elder and researcher with extensive experience in the Selwyn and Mackenzie Mountains. Andrew lives in Norman Wells, and has participated in the NWT Ice Patch Project since 2005. Naomi Smethurst is the Assessment Archaeologist with the Government of the Northwest Territories, based at the Prince of Wales Northern Heritage Centre in Yellowknife. Naomi has participated in the NWT Ice Patch Project since 2016. Thomas D. Andrews, PhD, is principal and co-owner of Spruceroot Group Heritage Consulting and former Territorial Archaeologist at the Prince of Wales Northern Heritage Centre in Yellowknife. Andrews has participated in the NWT Ice Patch Project since 2005.
References
1. Andrews, T.D., MacKay, G., Andrew, L. Archaeological Investigations of Alpine Ice Patches in the Selwyn Mountains, Northwest Territories. Arctic 65(5), 1-21 (2012).
2. Meulendyk, T., Moorman, B.J., Andrews, T.D., MacKay, G. Morphology and development of ice patches in Northwest Territories, Canada. Arctic 65(5), 43-58 (2012).
3. Ibid.
4. Galloway, J.M. et al. Diet and habitat of mountain woodland caribou inferred from dung preserved in 5,000-year-old alpine ice in the Selwyn Mountains, Northwest Territories, Canada. Arctic 65(5), 59-79 (2012).
5. Ng, T.F.F. et al. Preservation of viral genomes in 700-year-old caribou feces from a subarctic ice patch. Proceedings of the National Academy of Science 111(47), 16842-16847 (2014).
6. Letts, B. et al. Ancient DNA reveals genetic continuity in mountain woodland caribou of the Mackenzie and Selwyn Mountains, Northwest Territories, Canada. Arctic 65(5), 80-94 (2012).
7. Meulendyk, T. et al. Morphology and development of ice patches (2012).